Drug-related nephrotoxicity is a major cause of renal failure and limits the use of clinically important agents such as cisplatin, gentamicin, and cyclosporine. Unfortunately, the cellular basis of these cytotoxic actions is poorly understood. The present investigation will use a combination of in vitro and in vivo approaches to dissociate direct from indirect tubular effects and to identify specific physiological processes which are adversely affected by these three drugs. Five issues will be addressed: 1) By isolating proximal tubules, medullary thick ascending limbs (mTAL), and inner medullary collecting ducts (IMCD), we will identify nephron segments which are injured. Acute and chronic studies will evaluate the effects of direct drug additions to suspended cells as well as the physiological status of cells isolated from animals receiving in vivo treatment. 2) Ion-specific electrodes (K+ and Ca2+), an oxygen electrode, and biochemical assays will uncover drug-induced alterations in ion transport, cellular Ca2+ regulation, mitochondrial ATP production, and other cellular processes. 3) Using magnetic resonance spectroscopy (MRS) we will identify metabolites of these drugs and resolve their role in mediating toxicity. 4) By using in vivo magnetic nephrotoxin- mediated changes in renal metabolism and renal blood flow will be observed non-invasively. 31P MRS will be used to monitor in vivo changes in renal ATP, pH, and Mg2+. Furthermore, new magnetic resonance imaging (MRI) techniques will be used to image in vivo differences in regional fluid flow. These flow sensitive techniques can selectively highlight flow in large blood vessels or microcirculation. 5) With this knowledge of nephrotoxin-induced changes in renal function, therapies to reduce or prevent nephrotoxicity will be designed and investigated. Overall, these strategies offer an experimentally sound approach to identifying the basis of cytotoxic injury associated with these nephrotoxins.